Interference mitigation for positioning reference signals

ABSTRACT

Techniques are provided, which may be used for determining a position of a user equipment (mobile device). In certain example implementations, tones in positioning signals from one or more sources that may interfere with certain positioning signals be estimated and some form of interference mitigation may be applied, which may better enable the user equipment to acquire certain other positioning signals that may be useful in determining a position of the user equipment.

CROSS-REFERENCE TO PROVISIONAL APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalApplication No. 62/085,420 filed on Nov. 28, 2014 and entitled“INTERFERENCE ESTIMATION AND CANCELLATION FOR POSITIONING REFERENCESIGNALS”, which is incorporated herein by reference in its entirety.

FIELD

This patent application relates to techniques for use in determining, atleast in part, a position of a user equipment, and more specifically todevices and methods that may be used to mitigate (e.g., alter, reduce,cancel) interference in positioning signals received by the userequipment for use in positioning.

BACKGROUND

Long Term Evolution (LTE), defined in a standard known as 3^(rd)Generation Partnership Project (3GPP), describes a measurement by amobile device of a difference in times of arrival of signals from twobase stations. To enable detection of signals from multiple basestations, a signal in LTE is dedicated to positioning, known as apositioning reference signal (PRS). Each PRS signal contains a specificpattern assigned thereto, e.g. based on an identifier of a base station,known as the Physical Cell Identity (PCID or PCI). Tones in the PRSsignal may employ a frequency re-use factor of 6. The re-use factor maybe, for example, determined by v_shift=mod(PCID, 6). Two or more basestations with a common mod(PCID, 6) may transmit PRS tones whichcollide, causing interference. Scrambling codes may distinguish a PRSsignal from among multiple PRS signals received at a mobile device in acommon frequency bin, from multiple base stations having the samemod(PCID, 6). Use of scrambling codes may provide 20 dB (average) to 30dB (best case) isolation, which can be insufficient to overcome a powerdifferential due to distances of a mobile device from its serving celland the other cells. Such a power differential may cause PRS signalsfrom one or more base stations to drown in an elevated noise floor, andnot be detected.

SUMMARY

In accordance with certain aspects of the present description, it may berecognized that tones in positioning signals from one or more sources(e.g. base stations) that are sensed strongly (“strong positioningsignals”) may be estimated in a specific cyclical period (e.g. durationof a positioning occasion) that occurs in an LTE signal and mitigated inthe same specific cyclical period (e.g. within the same positioningoccasion), which may enable a mobile device or other such user equipment(UE) which performs the estimation and mitigation to measure one or moreadditional positioning signals that are sensed weakly relative to theone or more strong positioning signals.

In certain example implementations, a wireless transceiver in a userequipment may measure a plurality of positioning signals that aresynchronized relative to one another, to obtain initial positioningmeasurements. In the same user equipment, one or more processor(s) mayestimate a plurality of tones of one or more interfering station(s), (1)based on the initial positioning measurements measured in a currentcyclical period, and (2) based on identification of the one or moreinterfering station(s). The same one or more processor(s) mayadditionally mitigate at least one of the plurality of tones of one ormore interfering station(s), from the initial positioning measurementsmeasured in the current cyclical period (used in estimating theinterfering station(s) tones), to obtain modified positioningmeasurements.

Before, during, or after the above-described example interferenceestimation and mitigation process, the one or more processors maydetermine times of arrival, at the user equipment, of positioningsignals from the one or more interfering station(s), based at least onthe initial positioning measurements (e.g. in a normal manner ofprocessing positioning signals, in accordance with LTE). Additionally,after the above-described interference estimation and mitigationprocess, the one or more processors may determine times of arrival, atthe user equipment, of positioning signals from the one or more weakstation(s), based at least on the modified positioning measurements.Further, one or more processor(s) may use the arrival times of the oneor more interfering station(s) positioning signals and the arrival timesof the one or more weak station(s) positioning signals, to compute, atleast in part, a position of the user equipment.

In certain embodiments, one or more interfering stations may beidentified prior to the current cyclical period, for example, byapplying a test of interference to additional initial positioningmeasurements that may be measured in one or more earlier cyclicalperiod(s), e.g. based on signal-to-noise ratios (SNRs) of positioningsignals. Specifically, some embodiments may check whether asignal-to-noise ratio of a positioning signal from a strongest stationis greater than a first threshold and additionally check whether anothersignal-to-noise ratio of another positioning signal from another stationis less than a second threshold (e.g. noise threshold). In certainexample implementations, in response to having both the just-describedconditions met, the strongest station may be identified as aninterfering station, and the above-described example interferenceestimation and mitigation process or the like may be performed, e.g.,followed by position determination based on arrival times of strong andweak positioning signals. In certain example embodiments, should one ormore condition(s) fail to be met, such an interference estimation andmitigation process may not be performed. Hence, in such a case, positiondetermination may, for example, be based only on arrival times of strongpositioning signals (e.g. when positioning signals with SNRs above noisethreshold are at least three in number).

It is to be understood that several other aspects of the embodimentswill become readily apparent to those skilled in the art from thedescription herein, wherein it is shown and described various aspects byway of illustration. The drawings and detailed description below are tobe regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is an example wireless communications environment of a userequipment, in several described embodiments.

FIG. 1B illustrates, in a flow chart, acts performed by the userequipment of FIG. 1A, in some illustrative embodiments.

FIG. 1C illustrates, in timing diagrams, performance of operation 180 ofFIG. 1B (interference estimation and mitigation) within a singlecyclical period, with both acts 170 and 180 being performed in a singleuser equipment in some embodiments.

FIG. 1D illustrates, in a flow chart, acts performed by the userequipment of FIG. 1A, in some illustrative embodiments.

FIG. 2 illustrates, in a flow chart, some example acts that may beperformed by user equipment in certain embodiments, to perform PRSmeasurements, initially without and subsequently with, mitigation (e.g.,interference cancellation (IC)) of one or more positioning signals thatare strong relative to other positioning signals received by the userequipment.

FIG. 3 illustrates, in a graph, an example method for mitigatinginterference from a strong cell in certain embodiments.

FIG. 4 illustrates, in a flow chart, some example acts that may beperformed by user equipment 200 in certain embodiments, to estimatetones in a PRS signal of a strong cell, and mitigation of the tones infrequency domain, on a sub-frame basis.

FIG. 5A illustrates, in a flow chart, some example acts that may beperformed by user equipment 200 in certain embodiments, to estimatetones in a PRS signal from a strong cell in frequency domain.

FIGS. 5B and 5C illustrate a frequency-domain interpolation filter andits time-domain magnitude response respectively, in accordance withcertain example embodiments.

FIGS. 5D and 5E illustrate a 3-tap interpolation filter and itstime-domain response respectively, in accordance with certain exampleembodiments.

FIG. 5F illustrates a 11-tap interpolation filter, in accordance withcertain example embodiments.

FIG. 5G shows a time-domain response of the interpolation filter in FIG.5F, in accordance with certain example embodiments.

FIGS. 5H and 5I show an example of comparison between the channelimpulse response (FIG. 5H) and the resulting CIR after frequencyinterpolation (FIG. 5I), in accordance with certain example embodiments.

FIG. 6 illustrates an example of user equipment that can be used formitigation of tones in a positioning signal, in accordance with certainexample embodiments.

DETAILED DESCRIPTION

In certain instances, a specific example of a strong interfering cell inthe context of a PRS detection capability may be a serving cell of amobile device or user equipment (UE). A UE (e.g. UE 150 in FIG. 1A) mayselect a strongest base station (e.g. eNodeB 151A in FIG. 1A) of thestrongest cell in its surrounding environment to be its serving basestation (or serving cell). Compared to other neighboring cells (e.g.served by eNodeB 151I, and eNodeB 151N), a serving cell (e.g. served byeNodeB 151A in FIG. 1A) may typically be much stronger. Hence, inaccordance with certain aspects of the present description and asdescribed in greater detail herein, a frequency bin corresponding tov_shift value of the serving cell (e.g. eNodeB 151A in FIG. 1A) may beinterference limited, and a neighbor cell with the same v_shift value asthe serving cell may have poor detection rates. Moreover, in accordancewith certain aspects of the present description and as described ingreater detail herein, if a UE (e.g. UE 150 in FIG. 1A) is closer indistance to the serving cell (e.g. eNodeB 151A in FIG. 1A) relative toother cells with the same v_shift value, such interference problems maybe further aggravated. In contrast, in accordance with certain aspectsof the present description and as described in greater detail herein, ifa UE has a serving cell that is only a few dB's stronger than theneighboring cells with the same v_shift value, such interferenceproblems may be less severe.

In several aspects of described embodiments, a procedure for determininga UE's position includes identification of strong interfering cellsusing assistance information, as illustrated in FIG. 1B. Specifically,in an OTDOA session, a wireless transceiver 1050 (which is includedwithin a UE 150, see FIG. 6) performs an act 161 to measure positioningsignals that are synchronized relative to one another, to obtainmeasurements (“initial positioning measurements”). In certain instances,initial positioning measurements may comprise “raw positioningmeasurements”. Hence, as used herein, initial positioning measurementsmay comprise data that has been processed in some manner and/or datathat may be in an unprocessed form (e.g., raw). Depending on theembodiment, the initial positioning measurements may be stored in astorage device 1025, for subsequent use by one or more processor(s) 1010in UE 150. The one or more processor(s) 1010 in UE 150 may be configuredto use certain of the initial positioning measurements from wirelesstransceiver 1050, which are made within a cyclical period in atransmission schedule of positioning signals (e.g. made over a singlepositioning occasion), to determine position, as discussed below. Toobtain the initial positioning measurements, positioning signals may bemeasured by a wireless transceiver 1050 in an act 161 (FIG. 1B), frommultiple stations that use a common frequency shift (i.e. the samev_shift value), and likely to interfere with one another. The initialpositioning measurements made in a current cyclical period may be storedin a storage device 1025, for use by one or more processor(s) 1010, ininterference estimation and mitigation in operation 180, as describedbelow.

The strength of a positioning signal may depend on the distance of UE150 to a station (e.g. eNodeB) of that cell, propagation channel loss,antenna orientation, and shadowing effects, just to name a few examples.This information may not be known apriori to UE 150. It may berelatively safe to assume that a serving cell is the strongest cell inthe OTDOA cell list, however, in accordance with certain aspects of thepresent description, even this knowledge may be insufficient, to enablemitigation of strong PRS signals. If a PRS signal from eNodeB 151A (FIG.1A) of a strong cell (“strong PRS signal”) is only a few dB's strongerthan PRS signals from eNodeB 151I, eNodeB 151J, and eNodeB 151N ofneighbor cells, there may be little if any advantage obtained from someof the example PRS interference mitigation techniques presented herein,e.g., when use of a scrambling code delivers at least 20 dB isolation.

In an example illustrated in FIG. 1A, each of eNodeB 151A, eNodeB 151I,eNodeB 151J, and eNodeB 151N have the same v_shift value. Hence, a PRSsignal from a station (e.g. eNodeB 151A) is sensed very strongly(“strong positioning signal”) in UE 150 by a wireless transceiver 1050therein (see FIG. 6), in a particular positioning occasion (e.g. N_(PRS)consecutive subframes) that occurs at a periodicity of T_(PRS) of an LTEsignal, which interferes with and causes the PRS signals from otherstations (e.g. eNodeB 151I, eNodeB 151J, and eNodeB 151N) in the sameparticular positioning occasion to be drowned in noise. Hence, UE 150may be configured to perform all acts of interference estimation andmitigation in operation 180 on measurements made within a singlecyclical period (e.g. a positioning occasion of a PRS signal which mayconform to LTE, and in this example the duration of the positioningoccasion may be a predetermined number of subframes N_(PRS)).

More specifically, the duration of a cyclical period, over which initialpositioning measurements made by wireless transceiver 1050 are used bythe one or more processor(s) 1010 to perform interference estimation andmitigation in operation 180, can be different. In an example illustratedin FIG. 1C, positioning occasions may occur in a transmission schedulein accordance with LTE, with a periodicity of T_(PRS), whereby a firstsubframe of one positioning occasion is separated from the firstsubframe of a next positioning occasion by T_(PRS) subframes. The periodT_(PRS) is defined in 3GPP TS 36.211, and can be, for example, 160, 320,640, or 1280 subframes (or milli-seconds), depending on theimplementation. In an example shown in FIG. 1C, interference estimationand mitigation in operation 180 is performed in two subframes, which areboth included in a cyclical period of N_(PRS)=2 subframes that occurconsecutively, and form a single positioning occasion. AlthoughN_(PRS)=2 is illustrated in FIG. 1C, the predetermined number N_(PRS)can be 1, 2, 4 or 6 subframes, in other such examples.

In several embodiments, one or more processor(s) 1010 in a UE 150 (FIG.1B) are configured to perform operation 180 which includes acts 182 and184, followed by a position determination in operation 190 whichincludes acts 192 and 194, as follows. Specifically, operation 180 usesinitial positioning measurements from wireless transceiver 1050, whichmay be made within a cyclical period (also called “current cyclicalperiod”) by wireless transceiver 1050 in UE 150, as follows. In act 182,the one or more processor(s) 1010 estimate tones of one or moreinterfering station(s), based on the just-described initial positioningmeasurements (e.g. obtained from storage device 1025), and based onidentification of the one or more interfering station(s) (which may alsobe obtained from storage device 1025). Depending on the embodiment, act182 may include, for example, one or more of: scaling, pruning andnoise-thresholding. Thus, in certain embodiments, an interferingstation's tones may be reconstructed in act 182, e.g. based onassistance information (e.g. without modeling an interfering station'spositioning signal within UE 150).

Thereafter, in an act 184, the same one or more processor(s) 1010 withinUE 150 cancel (or reduce or alter) the tones of the one or moreinterfering station(s) (obtained by reconstruction in act 182) from thesame initial positioning measurements which were measured in the currentcyclical period (and used in estimating the interfering station(s)tones), to obtain modified positioning measurements of the currentcyclical period. In some embodiments, acts 182 and 184 are performed ina sequential manner, one after another, on initial positioningmeasurements measured in a single subframe, e.g. stored in a copy of asample buffer in storage device 1025, so that on completion of act 184this copy stores modified positioning measurements. As illustrated inFIG. 1C, in some embodiments, acts 182 and 184 may be repeated, withmodified positioning measurements obtained after the repetition beingintegrated with modified positioning measurements in the previoussubframe.

Referring back to FIG. 1B, the modified measurements (stored in storagedevice 1025) are used by the one or more processor(s) 1010 in a positiondetermination operation 190, which includes acts 192 and 194. In an act192, the one or more processor(s) 1010 determine times of arrival ofpositioning signals of weak station(s) at UE 150, based modifiedpositioning measurements output by act 184. Additionally, in an act 174,which may be performed at any time after performance of act 161, the oneor more processor(s) 1010 use the initial positioning measurementsmeasured in the current cyclical period (e.g. stored in a sample bufferin storage device 1025), to determine times of arrival of positioningsignals of interfering station(s) at UE 150. The arrival times ofpositioning signals of the weak station(s) obtained from act 192 (FIG.1B) and the arrival times of positioning signals of the interferingstation(s) obtained from act 172 (FIG. 1B) are used in an act 194 (FIG.1B), e.g. to determine position of UE 150 in a normal manner, followedby storing the position in memory 1035 (FIG. 6), which may beimplemented as any non-transitory memory.

Accordingly, in some embodiments of UE 150 (FIG. 1A) of the typedescribed herein estimate the strongest PRS signal (e.g. from eNodeB151A with PCID 6) within the specific period N_(PRS) (e.g. in apositioning occasion, as shown in FIG. 1C), and also mitigate (e.g.cancel, reduce or alter) the strongest PRS signal (e.g. from eNodeB 151Awith PCID 6) within that same specific period N_(PRS) (e.g. in the samepositioning occasion, as shown in FIG. 1C). FIG. 1C additionallyillustrates an operation 170 of identification of strong positioningsignals, which may be marked as interfering signal(s) in someembodiments, based on measurements of positioning signals in one or morecyclical periods (e.g. occasion I−1), which occur prior to a currentcyclical period (e.g. occasion I) in which an operation 180 ofinterference estimation and mitigation is performed as described above.

More specifically, as illustrated in FIG. 1D, in an act 172, the one ormore processor(s) 1010 apply a test of interference to the initialpositioning measurements that are made within an earlier cyclical period(e.g. occasion I−1), to identify as interfering, one or more station(s)identified in a list received in assistance information. For example, inact 172, a strongest station in the initial positioning measurements maybe identified as interfering, when one or more first threshold(s) Th1are exceeded by signal-to-noise ratio(s) of positioning signals from thestrongest station and when one or more second threshold(s) Th2 are abovesignal-to-noise ratio(s) of positioning signals from one or more weakstation(s), with all these station(s) being identified in the list.

When both the just-described conditions are met, one or more strongeststation(s), which meet the first threshold-testing condition (based onTh1), may be identified as interfering station(s), and then interferenceestimation and mitigation in operation 180 is performed. When both theabove-described threshold-testing conditions are not met (e.g. if onlyone of these two conditions is met), interference estimation andmitigation in operation 180 may not be performed, and in such a case,position determination in act 194 may be based only on arrival times ofstrong positioning signals (e.g. when positioning signals with SNRsabove noise threshold are at least three in number). Therefore, in suchembodiments, the result of act 172 (FIG. 1D) is used to enable ordisable the operation 180. Thus, in several such embodiments, a strongsignal may be identified (or not identified) as an interferer, inoperation 170 (FIG. 1C) which is performed at the beginning of a sessionto determine position, e.g. within the first one or two occasions, whichmay be occasions I−1 and I−2, and during operation 170 all measurementsare made in a normal manner (and no attempt is made by processor(s) 1010to estimate, reconstruct and mitigate (e.g. cancel, reduce or alter)interference).

During such an operation 170 (FIG. 1D), some embodiments of processor(s)1010 may estimate the SNR of each positioning signal, compare theseestimated SNRs using the above-described two threshold-testingconditions (based on thresholds Th1 and Th2), to determine and mark anypositioning signal(s) as “strong” interferers, which need to bemitigated (e.g. cancelled, reduced or altered) in operation 180. Inperforming the operation 170, for the second threshold-testing condition(based on noise threshold, e.g. Th2) to be satisfied, processor(s) 1010may not need an accurate SNR estimation of weak positioning signal(s).Specifically, when a positioning signal is above noise floor (e.g. Th2),then processor(s) 1010 is configured to determine that this positioningsignal's SNR is reliable, which is then used in ranking positioningsignals, for use in identifying one or more strong signal(s) by use ofthe first threshold-testing condition (based on threshold Th1). One ormore such highest ranked positioning signal(s) may be identified byprocessor(s) 1010 as interfering in operation 170, for use ininterference mitigation in operation 180, when the secondthreshold-testing condition is also met, by at least one positioningsignal. When a positioning signal is equal to or below the noise floor(e.g. drowned in noise), processor(s) 1010 is configured to determinethat the SNR value of this positioning signal is equivalent to noiseSNR, and in this case the second threshold-testing condition (based onthreshold Th2) is determined to be met.

In some embodiments, prior to act 172 (FIG. 1D), processor(s) 1010 in UE150 may obtain assistance information in a normal manner, e.g. from acomputer 100 (FIG. 1A) that supports one or more centralized functions(e.g. OA&M computer). The assistance information may include, forexample, a list of neighbor cells (OTDOA cell list) with detailedinformation about their PRS configuration, PCI, and expected delay andsearch window with respect to a reference cell. Receipt of assistanceinformation by UE 150 facilitates PRS processing and Reference SignalTime Difference (RSTD) measurement at UE 150, e.g. as time difference ofarrival (TDOA) between two PRS signals. Moreover, in some embodiments,after act 172 (FIG. 1D), processor(s) 1010 in UE 150 may perform act174, to determine arrival times of the positioning signals fromstation(s), which were identified as interfering in act 172.

Act 172 (FIG. 1D) may be followed by operation 180 (FIG. 1D) which issimilar or identical to operation 180 (FIG. 1B) described above, exceptfor the following. Specifically, in some embodiments, act 182 and act184 are performed on initial positioning measurements made in a singlesubframe (e.g. subframe #3 of occasion I shown in FIG. 1C), and in anact 185, processor(s) 1010 in UE 150 may integrate the modifiedpositioning measurements obtained from act 184 with correspondingmodified positioning measurements obtained from an earlier iteration ofact 184, if there was a previous subframe (when there is no earlieriteration, and no previous subframe, no integration is done).Thereafter, in an act 186 (FIG. 1D), processor(s) 1010 in UE 150 maycheck if all subframes in the current occasion I have been processed andif not, return to the act 182 (described above). When all subframes inthe current occasion I have been processed, the answer in act 186 isyes, and processor(s) 1010 may perform position determination inoperation 190, by performing the acts 192 and 194.

Hence, based on PRS interference mitigation, by position determinationin operation 190, UE 150 measures an arrival time τ_(j) of the PRSsignal from eNodeB 151J with PCID 18, by mitigation of the strongest PRSsignal (e.g. within a fraction of cyclical period T_(PRS)). Also whilemitigating (e.g. by cancelling, reducing or altering) the strongest PRSsignal (e.g. within the fraction of cyclical period T_(PRS)), UE 150measures the arrival times τ_(i) and τ_(n) of the PRS signals fromeNodeB 151I (with PCID 0) and eNodeB 151N (with PCID 12). At this stage,in some embodiments of act 192 (FIG. 1B), UE 150 may compute three TimeDifference of Arrival values, τ_(i)−τ_(j), τ_(i)−τ_(n), and τ_(i)−τ_(a)(this last TDOA value being based on measurement of an arrival timeτ_(a) of the PRS signal (which is the strongest PRS signal) from eNodeB151A with PCID 6, measured in the same cyclical period T_(PRS) prior tomitigation), which are used as RSTDs, to compute the position of UE 150in a normal manner.

In some embodiments, operations related to a subframe N's sample bufferare performed by processor 1010 during a time period in which subframeN+1 is being received by wireless transceiver 1050. In such embodiments,estimation in act 182 (FIG. 1D) is performed based on initialpositioning measurements made by wireless transceiver 1050 in the entiresubframe N, and mitigation in act 182 (FIG. 1D) is also performed on theinitial positioning measurements made by wireless transceiver 1050 inthe entire subframe N.

In an illustrative example shown in FIG. 1C, each occasion I has twosubframes. In this example, during occasion I, while subframe 3 is beingreceived in positioning signals at UE 150, wireless transceiver 1050measures the positioning signal of each station therein normally.Moreover, in this example, in occasion I−1, while subframe 4 is beingreceived at UE 150, wireless transceiver 1050 measures each station'spositioning signal normally, and in operation 170 processor 1010integrates the initial positioning measurements in the subframe 4 withinitial positioning measurements in the previous subframe, i.e. subframe3. Furthermore, at any time after occasion I−1 occurs in the timingschedule of positioning signals being received at UE 150, processor 1010may identify strong positioning signals in operation 170, for use inmitigation to be performed in operation 180. In the followingdescription, assume one strong positioning signal is marked formitigation in operation 170. At this stage, processor 1010 may performact 172 (FIG. 1D) to estimate the TOA of the strong positioning signal(assume TOA of a weak positioning signal is not possible to estimate,due to its SNR being below noise threshold, e.g. Th2).

Subsequently, in the just-described illustrative example, in occasion I(FIG. 1C), while subframe 3 is being received at UE 150, wirelesstransceiver 1050 measures the strong positioning signal normally, and ina first iteration of act 182 and act 184 (FIG. 1D) processor 1010reconstructs the strong positioning signal's tones and mitigates (e.g.cancels, reduces or alters) the estimated tones of the strongpositioning signal from the sample buffer, and in this manner measuresthe weak positioning signal (and these results may be stored in storagedevice 1025, as modified positioning measurements of subframe 3). Then,in occasion I (FIG. 1C), while subframe 4 is being received at UE 150,wireless transceiver 1050 measures the strong positioning signalnormally, and in a second iteration of act 182 and act 184 (FIG. 1D)processor 1010 reconstructs the tones of the strong positioning signal,and mitigates (e.g. cancels, reduces or alters) these reconstructedtones from the sample buffer, and in this manner again measures the weakpositioning signal, and integrates these results (i.e. modifiedpositioning measurements of subframe 4), with subframe 3's modifiedpositioning measurements (previously stored in storage device 1025,during receipt of an earlier frame that contained subframes 3 and 4 ofoccasion I). After occasion I (FIG. 1C), in act 192 (FIG. 1D) processor1010 estimates the TOA of the weak positioning signal (and may updateTOA of strong positioning signal, if needed again). Then, act 194 (FIG.1D) is performed to use the TOAs of strong and weak positioning signalsto compute a position, as described above.

As illustrated in FIG. 2, in an act 201, several described embodimentsof UE 200 of the type described above (e.g. UE 150) is designed tomeasure PRS signals from all base stations identified in the OTDOA celllist, in a normal manner. A normal manner of processing of PRS signalsin UE 200 may be different in different implementations, based on theconfiguration of the PRS signal as specified in the 3GPP standard (whichdoes not specify any implementation). Act 201 of some embodiments mayinclude processing of PRS signals being measured to obtain PRS symbols(i.e. symbol processing), and/or may include obtaining tones at multiplefrequencies (also called PRS tones). In certain embodiments of the typedescribed herein, any existing normal flow of processing PRS signals infrequency domain (e.g. descrambling, combining repeated tones andde-staggering) may be modified, to store in a buffer 212 innon-transitory computer-readable memory an estimate of the frequencydomain channel response and/or store in another buffer 211 an estimateof time-domain channel impulse response (CIR) of each base station, asgenerated from the received PRS signals.

Specifically, in some embodiments, channel impulse response in buffer211 is obtained by an inverse fast fourier transform (IFFT) to thefrequency domain channel response in buffer 212, which is measuredduring normal PRS processing in act 201 (FIG. 2). Depending on theembodiment, either frequency domain channel response stored in buffer212 or time domain CIR stored in buffer 211 (FIG. 2) both innon-volatile memory, e.g. memory 1035 (FIG. 6) may be used as inputsubsequently, while continuing to measure PRS signals within a specificperiod, to simultaneously estimate and mitigate (e.g. cancel, reduce oralter) one or more tones of one or more strongest base stations in act206 (FIG. 2) successively. One of the advantages of storingfrequency-domain channel response in buffer 212 in act 201 is to savecomputational complexity in a frequency domain interference estimationmethod as shown in FIG. 5A (thereby to avoid using a FFT or DFT in act413 in FIG. 4).

After processing of PRS signals in act 201, an act 202 is performed byUE 200 in embodiments of the type described herein, to identify astrongest base station in each frequency bin, based on normal processingof PRS signals in act 201. In some embodiments of act 202, a metric ofsignal-to-noise ratio (SNR) in the PRS signal may be computed by UE 200for each base station, and base stations in a group (with a common PCIDmod 6 value) may be ranked based on SNR to form a list, with thestrongest base station being ranked first in the list. One example of anSNR metric that may be computed by UE 200 in certain describedembodiments is based on channel energy response (CER), which in turn maybe required for normal PRS processing, e.g. to detect earliest arrivalpath (EAP) of each base station. Channel energy response (CER) may beobtained by squaring the magnitude of the channel impulse response (CIR)211. Another example of an SNR metric of the PRS signal that may becomputed by UE 200 of some described embodiments is Reference SignalReceived Power (RSRP), which in turn may be required for normal PRSprocessing in other implementations. Any other SNR metric may be used toidentify the strongest base station in act 202, depending on theembodiment.

Thereafter, in acts 203 and 204, UE 200 may be designed (e.g. inhardware or software or a combination thereof) to check whether twoconditions are satisfied, which may be checked in any order relative toone another, as follows. A first condition is whether the SNR metric ofthe PRS of the strongest base station (“strongest PRS signal”) isgreater than a first threshold, Th1. A second condition is whether theSNR metric of the PRS of any other base station in the frequency bin(with the same PCID mod 6 value as the strongest base station) is lessthan a second threshold Th2. When both conditions are met, specificallyif within each group, the SNR metric of the PRS of the strongest basestation (first in the list) is higher than the first threshold Th1 andthere exists at least one other neighbor base station in that same groupwith SNR metric less than the second threshold Th2, then UE 200 may bedesigned to perform act 205. In act 205, the strongest base stationwithin this group is marked in memory (e.g. see memory 1035 in FIG. 6)for mitigation of one or more tones of strong base station(s) (referredto herein as “interference”), followed by checking whether all groups(with different PCI mod 6 values) have been processed (see act 208 inFIG. 2, described below).

Values of thresholds Th1 and Th2 may be determined by experimentation,based on the specific method of processing PRS signals and interferencemitigation chosen for implementation, and its range of reliableperformance Guidelines to determine approximate values of thresholds Th1and Th2 are described below, for some illustrative embodiments.Threshold Th2 depends on a detection threshold of the PRS signal in anormal flow of processing the PRS signal in act 201 (withoutinterference mitigation), and a value of the SNR metric at which the UEdeclares detection of a base station. The detection threshold ispredetermined, based on a tradeoff between desired detection rate ofreal base stations and false alarm rate of bogus base stations or unrealpath of a real base station. Very high detection rates of real basestations and very low false alarm rates are both desired, but in orderto achieve very low false alarm rates, the detection threshold needs tobe set high, which in turn may lower detection rates. In practice, adetection rate of >90% and false alarm rate of <1% is pursued and thedetection threshold is adjusted towards that.

Threshold Th2 may be set to be directly equal to detection thresholdused in the normal flow of processing the PRS signal. If so, iteffectively means that any base station not detected (below detectionthreshold) triggers one of the conditions shown in acts 203 and 204 inFIG. 2, thereby marking the strongest base station for PRS interferencemitigation in act 205. In practice, it is possible to add an offset of afew dBs to the detection threshold, to obtain threshold Th2. If so, itmeans that even base stations above the detection threshold may triggerone of the conditions in FIG. 2. These base stations may already bedetected in act 201 without PRS interference mitigation; however,reliability of measurement of the PRS signal may be increased whenestimation and mitigation of a strong tone or multiple strong tonessuccessively is done in act 206 (described below).

Threshold Th1 may be selected based on the value of threshold Th2 andaverage code isolation between scrambling codes of two base stationswith different PCIDs. Based on a standard's description of thescrambling code, there may be 20 dB of average code isolation betweentwo different base stations. Maximum isolation in some cases may be asmuch as 30 dB and minimum isolation can be as low as 17 dB. Oneinterpretation of this isolation may be that in the presence of a strongbase station, the noise floor is on average 20 dB below the SNR of thePRS of the strong base station (SNR of the “strong PRS signal”) and maybe determined by its interference, as opposed to background thermalnoise. Hence, any other neighbor base station which is 20 dB weaker thanthe strong base station may remain undetected during normal processingof the PRS signal.

Typically, several described embodiments may set threshold Th1 asthreshold Th2 plus an offset, where this offset depends on thereliability of the method chosen for PRS interference mitigation andalso depend on the average (or minimum) code isolation. As an example,in a discovery phase in act 201 (FIG. 2), if only two base stations arefound to be in the first frequency bin (corresponding to v_(shift)=0(e.g, PCID0 and PCID6) and the SNR of the PRS of PCID0 and PCID6 arefound to be 30 and 26 dB, respectively, after the discovery phase in act201, there is no need to mark PCID0 for interference mitigation in act205, because PCID6 is already well above the detection threshold.However, if SNR of the PRS of PCID6 is measured to be only 15 dB, thenin an act 205, PCID0 is marked in memory, for interference mitigation.

Subsequently, in an act 206 that is performed in some embodiments in thesame subframe as performance of act 201, UE 200 may be designed (e.g. inhardware or software or a combination thereof) to continue to measurethe PRS signal in the subframe while simultaneously mitigating (e.g.cancelling, reducing or altering) one or more tones of strong PRSsignal(s) estimated in the subframe (i.e. interference in other PRSsignals by PRS signal(s) of one or more strong base station(s)), e.g.PCID0. Subsequently, in an act 206A, UE 200 checks if all stations inthe list (see act 201) have been detected, and if so goes to act 207 andif not returns to act 202 (thereby to repeat the above-described acts202-206, for another strongest station). Note that although estimationof strong PRS signal(s) and mitigation of the strong PRS signals whilecontinuing to measure PRS signals has been described in this paragraphas occurring in a common subframe in some embodiments, other embodimentsmay be implemented using slower hardware wherein the estimation andmitigation are performed within two or more consecutive subframes (overa specific cyclical period) that occur in a common positioning occasion(also called PRS occasion) in a transmission schedule of period T_(PRS).

When there are two strong interfering cells in a group, the strongeststation is estimated and its effect is mitigated (e.g. cancelled,reduced or altered) first in a specific positioning occasion, and then asecond strongest station is estimated and its effect is mitigated (e.g.cancelled, reduced or altered) next in the same specific positioningoccasion, and so on until no more strongest stations are detected inwhich case the branch 206B is taken to act 207. Thereafter, in an act207 (FIG. 2) performed by UE 200, the PRS measurement of the strongestbase station, e.g. PCID0 (obtained in act 201) and the PRS measurementof one or more other base stations e.g. PCID6 (obtained in act 206 withmitigation or in act 201 without mitigation, depending on the conditionsin acts 203 and 204) are used to determine the Reference Signal TimeDifference (RSTD). The RSTD is thereafter used in a normal manner, todetermine a position of the UE.

Acts 202-205 described above may be performed by UE 200 of someembodiments (“sequential embodiments”) for a group of base stationssequentially, and repeated in a loop over multiple groups (e.g. 6groups, wherein all base stations within a group have a common PCID mod6 value), or alternatively the acts 202-205 may be performed by UE 200in certain embodiments (“parallel embodiments”) in parallel relative tothese same acts 202-205 being simultaneously performed by UE 200 forother groups. In sequential embodiments, an act 208 may be performed byUE 200, after acts 203 and 204 are performed, to check if all groupshave been processed and if not by UE 200 returning to act 202. Moreover,an act 209 may be performed (e.g. after act 208) in sequentialembodiments, to check if any base station was marked for interferencemitigation in memory, followed by act 206 in which interference of themarked base station is estimated (to obtain “interfering tones”),followed by re-measurement of the PRS signal with mitigation of theestimated interfering tones of the marked base station.

Act 206 may be implemented by interference estimation in operation 410and interference mitigation in operation 420 (FIG. 4) in someembodiments, while certain other embodiments may implement the act 206by interference estimation in operation 510 (FIG. 5A) followed byinterference mitigation in operation 420 (FIG. 4). The specific mannerin which operation(s) 410, 420 and 510 are implemented may be different,depending on the embodiment. When no base station in any group is markedfor interference mitigation in act 205 (e.g. when either of theconditions in act(s) 203 or 204 is not met), then as shown by branch210, act 207 may be performed with the PRS measurements made in act 201.

In certain example implementation, it may be noted that PRS subframesmay be sparse (unlike CRS). Specifically, the distance between PRSoccasions is T_(PRS) with minimum periodicity of 160 ms. Consequently,it is not possible to use any measurements of PRS (such as a CIR or CERvector) from a previous PRS occasion for interference mitigation in apresent PRS occasion. Hence, channel estimation and interferencemitigation in act 206 is not staggered relative to act 201, and insteadin several embodiments, act(s) 201 and 206 are performed within the samesubframe. The ultimate goal of user equipment, e.g. UE 200 is to be ableto detect as many neighbor base stations as possible. As long as the EAPof a weak neighbor base station is accurately estimated by UE 200, thepurpose is served. Interference mitigation of PRS in act 206 of someembodiments may improve the detection rate of weaker neighbor basestations that may be overpowered by stronger interfering base stationsdetected in act 201.

Act 206 may be implemented in different ways, depending on theembodiment. For example, some methods to mitigate interference from oneor more strong base station(s) during processing of the PRS signal, mayinclude: zero forcing (nulling) using more than one receive chains (asillustrated in FIG. 3), time-domain (TD) interference estimation andmitigation in frequency domain (FD) (as illustrated in FIG. 4), andfrequency-domain (FD) interference estimation and mitigation (asillustrated in FIG. 5A). It should be understood that terms such as“mitigate”, “mitigation”, mitigating, or the like as used herein withregard to interference, are intended to represent one or more actionsthat affect all or part of one or more interfering aspects of one ormore signals such that all or part of some potential for signalinterference may be altered, reduced, or possibly even eliminated. Eachof these three methods is described below, in reference to thecorresponding figures.

In a method of zero forcing, Y is a vector of size N×1 denoting a set ofPRS signals being transmitted from N distinct transmit antennas. In FIG.3, a vector H denotes the M×N channel matrix modelling propagationeffects from each of the N transmit antennas to any one of the M>1receive antennas. The received signal R can be written asR=HY+Nwhere N is an additive noise vector. The receiver (e.g. UE 200)multiplies the received signal with a vector w which can achievedifferent means by design. A maximum ratio combining (MRC) can beachieved by setting=H^(H). The zero-forcing receiver (e.g. at UE 200) isgiven byW=(H ^(H) H)⁻¹ H ^(H)In vector space analogy with two sensors, the effect of zero-forcing andits opposite (beamforming) is illustrated in FIG. 3. Choosing W enhancesthe source (beamforming) and choosing W′ nulls the source out(interference nulling). In interference mitigation of the PRS signal,zero forcing requires at least two receive chains for mitigation of onestrong interfering base station. In so doing, the gain of receivediversity may be exchanged for nulling the interference. In the case oftwo strong interfering users, 4 receive chains are needed by extension.

Another method used in some embodiments (“TD estimation embodiments”) isinterference estimation in the time domain, and interference mitigationin the frequency domain. Time domain interference estimation may beachieved in TD estimation embodiments by improving the quality ofchannel estimation in values of a vector in the time domain thatrepresents the channel impulse response (CIR vector) 211. Quality of theCIR vector may be improved by scaling, noise-thresholding and pruning toobtain an improved CIR vector. PRS tones that are strongest (and henceinterfering with weaker tones) may be obtained in some TD estimationembodiments taking a fast fourier transform (FFT) of the improved CIRvector, i.e. by going to the frequency domain. As will be readilyapparent in view of this detailed description, instead of a fast fouriertransform, a discrete fourier transform (DFT) may be used in other TDestimation embodiments. Mitigation of the strongest (i.e. interfering)tones may be accomplished in the frequency domain, in various TDestimation embodiments.

Interference mitigation of the PRS signal may be performed at a subframelevel in some embodiments (as opposed to occasion-basis). Specifically,channel impulse response in buffer 211 (FIG. 2) may be processed in amethod 400 of FIG. 4 that implements the act 206 of FIG. 2 in certain TDestimation embodiments, as follows. In method 400, UE 200 may bedesigned to perform an operation 410 of interference estimation in timedomain, followed by an operation 420 of interference mitigation.Interference estimation in operation 410 may include act 412 of scaling,followed by pruning (also referred to as windowing), cleaning, and zeropadding the time-domain CIR estimate in buffer 211 (saved by act 201 inFIG. 2 as a CIR vector), to improve quality of channel estimation inlower regions of SNR.

A scaling operation performed in act 412 (FIG. 4) may take the form ofscaling each value in the CIR vector with its relative signal strength(RSS) over signal-plus-noise level, to obtain a scaled CIR vector. Assuch, the noisy values in the CIR vector are further attenuated in thescaling operation, without attenuating the values that have highrelative signal strength, thereby improving the quality of the CIRvector.

A windowing (or pruning) operation also performed in act 412 is based onat least two inputs, namely WIN_CENTER and WIN_SIZE that are received asinputs. Window center (WIN_CENTER) is used to center the window of thescaled CIR to be included, while pruning the rest. The size of thewindow (WIN_SIZE) is the number of CIR elements on either side ofWIN_CENTER that may be included while pruning the rest. One method toobtain the WIN_CENTER parameter is by finding the strongest peak in theCIR vector (e.g. CER=|CIR|^2, and identifying a maximum value therein).WIN_SIZE can be assigned to take the expected value of the channel delayspread, e.g. 4 micro-seconds as described in the second paragraph below.Alternatively, the WIN_CENTER can be obtained by translating theexpected received signal time difference (RSTD) of the cell, which isfurnished to UE by the network assistance data. WIN_SIZE can be obtainedby translating the expected RSTD uncertainty, which is also furnished toUE by the network assistance data.

A cleaning operation also performed in act 412 (FIG. 4) includesnoise-thresholding, which may take the form of comparing the energy ofeach value in the windowed CIR vector, with a predetermined threshold(supplied as input to the cleaning operation), and zeroing out a value(also called “tap”) in the windowed CIR vector, if it does not exceedthe predetermined threshold. The predetermined threshold may bedetermined in one embodiment as X dB below a maximum value of the CERvector, where X is predetermined to be either equal to, or slightlymore, than a detection threshold of the PRS signal, in a normal flow ofprocessing the PRS signal in act 201 (discussed above).

Further, the cleaning operation in act 412 of some embodiments includeszero-padding, which zeroes out all but regions where the majority of theenergy (more than 50% of energy) of the CIR vector resides.Specifically, in such embodiments, all possible multipath profiles areexpected not to exceed a predetermined value of delay spread (e.g., 4μs), and therefore only the 4 micro-seconds of values around thestrongest peak in the windowed CIR vector are retained and the rest arereplaced by zeros (i.e. pruned), to obtain a pruned CIR vector. Thedelay spread can be heuristically assigned to be a certain fixed value,based on a conservative assumption of worst-case scenarios. It does notneed to be exact. A conservative approximation works well.

A zero padding operation performed in some embodiments of act 412 (FIG.4) is equivalent to adding zeros to either or both sides of the prunedCIR vector such that the output vector (input to the FFT stage in act413, described next) is equivalent to FFT size. For instance, if theoutput length of the pruned vector is 128 and the FFT stage next is ofsize 2048, then 2048-128 or 1,920 zeros are inserted to obtain animproved CIR vector. Zero padding is done in act 412 for elements (or“taps”) that are outside of the [WIN_CENTER−WIN_SIZE,WIN_CENTER+WIN_SIZE] range.

Thereafter, in act 413 (FIG. 4), the improved CIR vector resulting fromact 412 is transformed to the frequency domain, by applying a 2048-pointFFT. Depending on the embodiment, the size of FFT does not necessarilyhave to be 2048 and can be sufficiently large to cover the PRS signalbandwidth. Size 2048 is a size that covers all possible LTE bandwidthand is used in certain embodiments of act 413.

The FFT operation in act 413 (FIG. 4) may also take as input, a scalevalue which can be used in some embodiments, to additionally enhance thechannel estimate quality, by adjusting for energy difference in theprevious stage. The scale value is predetermined based on the number oftaps that survive act 412, relative to size of FFT. Interferenceestimation in operation 410 (FIG. 4) with or without scaling of animproved CIR vector (output by act 412 in FIG. 4), provides an estimateof interference in the PRS signal. The improved CIR vector (with orwithout scaling) is transformed into the frequency domain in act 413,for use in interference mitigation in operation 420 (described below).Estimation of PRS signal interference, by generation of the improved CIRvector (with or without scaling), is believed to be novel andnon-obvious.

Thereafter operation 420 of interference mitigation may be performed(based on the improved CIR vector), starting with acts 424A-424N (FIG.4) for each of N tones in the frequency domain, to reconstruct originalPRS tones, beginning on a symbol level basis. Specifically, thisoperation 420 may be repeated N times (performed once for each of the Ntones), where N depends on the cyclic prefix (CP) type (which can beeither Normal CP, abbreviated as NCP, or Extended CP abbreviated as ECP)and number of transmit (Tx) antennae (Ant) of the cell.

-   -   N=8 for NCP and 1-2 Tx Ant    -   N=7 for NCP and 4 Tx Ant    -   N=6 for ECP and 1-2 Tx Ant    -   N=5 for ECP and 4 Tx Ant

For each of N repetitions, the corresponding PRS tones may be fetched inparallel in acts 424A-424N (FIG. 4) from one or more non-transitorycomputer-readable storage media that may store the output of an FFToperation in act 413 (described above). The just-described PRS tones arefetched based on an offset determined by a v_shift value (which is afirst input), and scaled by a scaling coefficient (which is a secondinput) in acts 424A-424N, followed by rotation in acts 425A-425N in adirection opposite to the direction used in act 201 of FIG. 2(specifically, measuring PRS followed by symbol processing), andscrambled in acts 426A-426N with a corresponding seed (same seed as usedin act 201).

In particular, scaling operations in acts 424A-424N and rotationoperations in acts 425A-425N are performed for estimating interferenceto undo any corresponding scaling and rotation operations that wereperformed in normal PRS measurement in act 201. Specifically, scalingoperations in acts 424A-424N are the inverse of their counterparts inact 201. For example, in implementations wherein tones obtained from aPRS signal are scaled by a certain scaling factor during normal flow inact 201, the tones output by the FFT operation in act 413 are scaled inact(s) 424A by the inverse of that scaling factor (and this inverse isreferred to in the paragraph above, as the second input). The scalingfactor used in normal PRS measurement in act 201 of some embodimentsadjusts for a gain over a datapath, to take advantage of a dynamic rangeof a fixed-point implementation of the datapath.

Additionally in act 201, certain embodiments may null out, attenuate oramplify some PRS symbols, depending on their collision with otherchannels, such as Primary Synchronization Signal (PSS) and SecondarySynchronization Signal (SSS). Thus, in these certain embodiments, suchacts are performed in reverse, in the scaling operations of acts424A-424N.

The purpose of a rotation operation in normal PRS measurement in act 201is to account for timing shifts (e.g. due to drifts or adjustments thatmay be made by any time-tracking-technique implemented in userequipment, e.g. UE 200). Rotation or phase-ramping in the frequencydomain in acts 425A-425N (for use in interference mitigation of PRS) isequivalent to a shift in time domain (also called timing shift). Thevalues of time delays (or shifts) used in 425A-425N are specific to PRSsamples (which at most can happen once every 160 subframe). In suchembodiments, acts 425A-425N receive frequency and phase as inputs (tothe rotation operation). Translation of a time shift to frequency/phaserotation can be performed in any normal manner, readily apparent to askilled artisan based on common engineering techniques and formulaefound in any signal processing textbook.

As noted above, results of acts 425A-425N are descrambled in acts426A-426N with a seed which is input thereto (same seed as used in act201). Descrambling in acts 426A-426N yields as corresponding outputsthereof, N reconstructed PRS tones for each of N symbols and the Nreconstructed PRS tones (identifying a strongest cell) are stored in oneor more non-volatile computer-readable storage media, such as media427A-427N. The N reconstructed PRS tones (from the strongest cell) aresubtracted in acts 428A-428N from one or more symbols in buffer 429(which may contain tones that are currently being measured in the PRSsignal, as per act 201), to obtain and store in memory 1035, aninterference mitigated PRS signal (e.g. at the end of act 206 in FIG.2).

In some embodiments, front end frequency domain symbol(s) in buffer 429described above may be same as in buffer 212 that stores frequencydomain channel response of act 201 (FIG. 2). Alternatively, certainembodiments maintain a duplicate of this buffer, and performinterference mitigation (in acts 428A-428N) on the duplicated buffer,e.g. buffer 429, without changing the values in a buffer 212 that storesfrequency domain channel response (as per act 201 in FIG. 2). Inillustrative embodiments, buffer 212 stores N front end frequency domainsymbols, where N=8 for NCP and 1-and-2 Tx Ant, N=7 for NCP and 4 Tx Ant,N=6 for ECP and 1- and-2 Tx Ant, and N=5 for ECP and 4 Tx Ant. Thus,each symbol in buffer 212 has 2*N_RB PRS tones. In the illustrativeembodiments, the duplicated buffer, e.g. buffer 429 stores only 1 symbol(i.e. one symbol) for the frequency domain channel response, which is acombined output of the descrambled N symbols stored in buffer 212. Asnoted above, the interference mitigated PRS signal output by acts428A-428N includes tones from cells whose PRS signals are weakly sensedin UE 200, i.e. weaker than the strongest PRS signal (from the strongestcell), in any of one or more groups.

Thereafter, the interference mitigated PRS signal output by acts428A-428N (e.g. in buffer 429) may be processed in a normal manner ofprocessing the PRS signal, to detect tones of one or more weak cells.For example, the interference mitigated PRS signal may be scaled using ascaling factor that is used in normal PRS measurement in act 201 of someembodiments, to adjust for a gain over a datapath. Additionally, asnoted above in reference to act 201, certain embodiments may null out,attenuate or amplify some PRS symbols, depending on their collision withother channels, such as Primary Synchronization Signal (PSS) andSecondary Synchronization Signal (SSS). Also, as noted above, a rotationoperation of the type performed on normal PRS measurement in act 201 maybe performed on the interference mitigated PRS signal, e.g. to accountfor timing shifts, as normally made in user equipment, e.g. UE 200.

As noted above, one or more of operation(s) 410 and 420 of someembodiments may be performed in real time in an act 206 (FIG. 2), e.g.within a common subframe in a radio frame of an LTE signal or within aduration of two or more consecutive subframes that occur in a common PRSoccasion of period T_(PRS), while certain other embodiments mayimplement an operation 410 and/or an operation 420 (and therefore act206 of FIG. 2) in an offline manner based on values that are stored inreal time in buffer 212 and buffer 429, e.g. stored during the commonPRS occasion.

After the above-described operation 420 has completed, if a PRS occasionin which the operation 410 was started has not yet ended, theabove-described operation(s) 410 and 420 may be repeated once more inreal time, within the same cyclical period (e.g. same PRS occasion) asfollows. Such a repetition may use the interference mitigated PRS signalin buffer 429 (see bottom of FIG. 4), as input to interferenceestimation by replacing the CIR vector in buffer 211 (see the top ofFIG. 4), so that the real time repetition stores in media 427A-427N, aPRS signal of a strong cell that may be weaker than the strongest cellalthough stronger than other weak cells whose PRS signals are now storedin buffer 429, at the end of a first repetition during a common PRSoccasion. The just-described real time repetition may be performedmultiple times (by repeating the above-described acts in FIG. 4) withinthe same cyclical period (e.g. PRS occasion), to identify PRS signals ofmultiple cells that are weaker than the strongest cell.

Acts 424A-428A . . . 424N-428N of some embodiments are mirror images ofcorresponding operations done in normal PRS processing, and may besimilar or identical to acts performed to implement interferencemitigation for CRS signals although as noted above, measurements of PRSfrom a previous PRS occasion are not used in interference mitigation ina present (also called current) PRS occasion. Instead, interferencemitigation for identification of weak PRS signals of some embodimentsuses measurements made during the same (or current) PRS occasion. A PRSoccasion provides at least 160 ms to complete operation(s) 410 and 420,which duration is sufficient for interference estimation and mitigationas described herein, based on the speed of processors that are currentlyavailable.

In certain embodiments (“FD estimation embodiments”), interferenceestimation of operation 410 (FIG. 4) in the time domain may be replacedby a corresponding operation 510 (FIG. 5A) performed in the frequencydomain, as described below. In FD estimation embodiments, channelimpulse response in buffer 211 in the time domain which is stored inmemory by act 201 (FIG. 2) is used in act 511. Moreover, the frequencydomain channel response in buffer 212 in the frequency domain which isstored in memory by act 201 (FIG. 2) is used in act 512-515 (FIG. 5A) asfollows. Interference estimation in frequency domain in operation 510includes peak detection in act 511, phase ramp operation in act 512(circular shift to align peak to origin), interpolation of frequencydomain channel response in act 513, scaling in act 514, reverse phaseramp operation in act 515 (to circular shift interpolated CIR back tooriginal time axis), resulting in an interpolated FD channel response inbuffer 503 (FIG. 5A). Interpolated FD channel response in buffer 503which is output by operation 510 (FIG. 5A), is further processed in thefrequency domain by interference mitigation in operation 420 (FIG. 4).Each of the above-described act(s) 511-515 is described below.

Peak detection in act 511 may be performed in some embodiments, asfollows. Denote the estimated channel impulse response in buffer 211which is stored by act 201 (FIG. 2) as the CIR vector in the time-domainnamely CIR[n]. An estimation of channel energy response (CER) isobtained in act 511 by squaring in time domain, as follows:CER[n]=|CIR[n]|². Then, a position of a peak in the CER vector may bedetected, by searching in act 511 for a maximum value among all valuesstored in the time-domain CER vector, as follows:d=max_(n)CER[n]

Phase ramp operation in act 512 may be performed in certain embodiments,as follows. A designed interpolation filter may be approximatelyequivalent to a time-domain window, centered at the origin. Thus, thepurpose of act 512 is to circularly shift the estimated CIR to align thepeak (detected in act 511) to origin. The shifted CIR is denoted byx[n]=CIR[(n+d)mod N _(FFT)]Denote the frequency domain channel estimation as C[k] which is the FFTof CIR[n]. Moreover, we denote the FFT of x[n] as X[k]. Then the abovecircular shift in the time-domain is equivalent to a phase ramp (+d) inthe frequency domain as follows

${X\lbrack k\rbrack} = {{C\lbrack k\rbrack}{\mathbb{e}}^{{j2}\;\pi\frac{d}{N_{FFT}}k}}$

After frequency interpolation of X[k] in act 513 (discussed below), theoutput of the frequency domain channel interpolation is denoted by{tilde over (Y)}[k]. A reverse operation is performed in act 515 whichis equivalent to shifting the interpolated channel response back to theoriginal time axis as CIR[n]. The reverse circular shift is equivalentto a phase ramp (−d) as follows:

${\overset{\sim}{C}\lbrack k\rbrack} = {{\overset{\sim}{Y}\lbrack k\rbrack}{\mathbb{e}}^{{- {j2}}\;\pi\frac{d}{N_{FFT}}k}}$

The above {tilde over (C)}[k] is stored in a memory and is utilized asfollows. {tilde over (C)}[k] is the output from the FD interferenceestimation in operation 510, which will be the input to the interferencemitigation in operation 420 in FIG. 4 (described above). Specifically,the same interference mitigation in operation 420 is used afterfinishing the FD interference estimation in operation 510 (to estimatePRS interference tones in frequency domain).

Interpolation of the FD channel response in act 513 may be performed asfollows. Frequency interpolation is performed in some embodiments toeliminate aliasing. Specifically, the estimated frequency-domain channelresponse has zero magnitude at the frequency tones k, where

-   -   k=6i+mod(2+v_shift, 6) 0≦i<2N_(RB) for Normal CP and 1-2 Tx Ant    -   k=3i+mod(2+v_shift, 3), 0≦i<4N_(RB) for Normal CP and 4 Tx Ant    -   k=3i+mod(2+v_shift, 3), 0≦i<4N_(RB) for Extended CP and 1-2 Tx        Ant    -   k=3i+mod(2+v_shift, 3), 0≦i<4N_(RB) and k=6i+mod(4+v_shift, 6),        0≦i<2N_(RB) for Extended CP and 4 Tx Ant        where v_shift=mod(PCID, 6), and N_(RB) is the number of resource        blocks (RBs). These zero tones in frequency domain cause        aliasing in the time domain. In some embodiments, one out of        every six frequency tones is a zero tone for Normal CP and 1-2        Tx Ant. Its time interval between two adjacent aliasing pulses        is 2048×Ts/6=11.11 μs, where Ts=1/(15000×2048) second. For        Normal CP, 4 Tx Ant and Extended CP, 1-2 Tx Ant, one out of        every three frequency tones is a zero tone. So their time        intervals between two adjacent aliasing pulses is        2048×Ts/3=22.22 μs. For Extended CP and 4 Tx Ant, three out of        six frequency tones are zero tones. Due to its repeat pattern,        the time intervals between two adjacent aliasing pulses is 11.11        μs.

To eliminate aliasing pulses with the time interval of, for example11.11 μs, one possible frequency interpolation filter is a 6-tap filteras followsH ₆ [k]=⅙×[1 1 1 1 1 1]which calculates the average value over the near-by six tones. Thefrequency-domain interpolation filter and its time-domain magnituderesponse are shown in FIGS. 5B and 5C respectively. As shown in FIG. 5C,the time-domain response attenuates the 11.11 μs aliasing pulses. Otherpossible frequency interpolation filters are the convolution of H₆ anditself, e.g. H₆

H₆ yields a 11-tap triangular interpolation filter. Similarly, toeliminate 22.22 μs aliasing pulses, one possible frequency interpolationfilter is a 3-tap filter as follows.H ₃ [k]=⅓×[1 1 1]FIGS. 5D and 5E illustrate a 3-tap interpolation filter and itstime-domain response respectively. Also, other possible frequencyinterpolation filter is a convolution of H₃. The number of taps of thefrequency interpolation filter is summarized in Table 1 below, fordifferent PRS configurations.

TABLE 1 The length of frequency interpolation filter, k ≧ 0 PBCH antennaports Cyclic Prefix One or two Four Normal CP 6 + 5 k 3 + 2 k ExtendedCP 3 + 2 k 6 + 5 kAs an example, for normal CP and 1-2 Tx Ant, UE 200 may use a 11-tapinterpolation filter which is presented as follows and is illustrated inFIG. 5F.

${H\lbrack k\rbrack} = {\frac{1}{6} \times \left\{ \begin{matrix}{1 - \frac{k}{6}} & {0 \leq k \leq 5} \\{1 + \frac{k}{6}} & {{- 5} \leq k \leq {- 1}} \\0 & {otherwise}\end{matrix} \right.}$Note that the integral of the interpolation filter Σ_(k=−5) ⁵H[k]=1. Thefrequency domain channel interpolation Y[k] is the linear discreteconvolution between X[k] and H[k], for 0≦k≦N_(FFT)−1Y[k]=(X*H)[k]=Σ _(m=max{0,k−5}) ^(min{N) ^(FFT) ^(−1,k+5}) X[m]H[k−m]Due to guard carriers around X[k], the above linear discrete convolutionis the same as a circular discrete convolution between X[k] and H[k].Note that the PRS bandwidth can be as large as N_(RB)=100 for 20 MHz;while the maximum LTE downlink system bandwidth is N_(RB)=110. There are5 guard frequency tones on the lower-end of frequency band and 5 guardfrequency tones on the upper-end of frequency band. Therefore, theoperation shown above is equivalent to a multiplication between x [n]and h[n] in the time domain, where h[n] is the IFFT of H[k] with thelength of N_(FFT).

FIG. 5G shows the time-domain response of the interpolation filter h[n],of which the IFFT of H[k] is scaled with N_(FFT) to make h[0]=1. Asshown in FIG. 5G, the peak of h[n] is centered at n=0. Thus, the phaseramp (+d) in act 512 (FIG. 5A) circularly shifts the peak of CIR to n=0aligning with the designed h [n]. The phase ramp (−d) in act 515 (FIG.5A) reverses the circular shift of act 512 and moves the filtered CIRback to its original axis.

In some embodiments, scaling in act 514 may be performed as follows.Some of frequency tones do not have PRS pilots. Therefore, thefrequency-domain convolution described above diminishes the energy ofCIR, due to the inserted zero tones in the frequency domain. To overcomethe energy diminishment, several embodiments of UE 200 multiply aboosting scalar α to Y[k]. The scalar α depends on the number ofnon-zero PRS tones in the frequency domain. Denote there are K_(NZ)non-zero PRS tones out of 12 frequency tones in a resource block. Thenthe frequency interpolation needs to be multiplied with a scalarα=12/K_(NZ) to overcome the energy diminishment caused by zero tones.For example, the normal CP with one or two PBCH antenna ports has 10non-zero PRS tones out of 12 frequency tones within a resource block,which implies α=1.2. Table 2 below shows a common scaling coefficient αfor different CP and different numbers of PBCH antenna ports.

TABLE 2 The common scaling coefficient α for frequency interpolationPBCH antenna ports Cyclic Prefix One or two Four Normal CP 1.2 1.5Extended CP 1.5 2

Even with the above boosting scalar α, the energy of band edge tones andthe frequency tones around DC are still diminished due to the frequencyinterpolation. Therefore, a finer scaling operation is desired aroundthe band edge tones and the frequency tones near DC. The scalingcoefficients are cell-specific and vary over the frequency tones. Denotethe frequency interpolation filter is H[k] for k₁≦k≦k₂. For example, the11-tap interpolation filter in FIG. 5F has k₁=−5 and k₂=5. The designedinterpolation filter has the condition that its sum over all taps equals1.

${\sum\limits_{k = k_{1}}^{k_{2}}{H\lbrack k\rbrack}} = 1$

The procedure of frequency interpolation is a convolution between thefrequency-domain channel response X[m] and the interpolation filterH[m], for the frequency tones m within the PRS bandwidth, as follows:

${Y\lbrack m\rbrack} = {{\left( {X*H} \right)\lbrack m\rbrack} = {\sum\limits_{k = k_{1}}^{k_{2}}{{X\left\lbrack {m - k} \right\rbrack}{H\lbrack k\rbrack}}}}$Note that some frequency tones of X[m] are zero. Hence, to maintain theenergy level from X[m] to the interpolated Y[m], a scalar coefficientα[m] is calculated as follows

${\alpha\lbrack m\rbrack} = {1/\left( {\sum\limits_{\underset{{X{\lbrack{m - k}\rbrack}} \neq 0}{k = k_{1}}}^{k_{2}}{H\lbrack k\rbrack}} \right)}$Therefore, the final output of the frequency interpolation is α[m]Y[m].

FIGS. 5H and 5I show an example of comparison between the channelimpulse response (FIG. 5H) and the resulting CIR after frequencyinterpolation (FIG. 5I). As shown in FIGS. 5H and 5I, the aliasing termsare diminished by the frequency interpolation.

In several embodiments of the type described above, a frequency-domaininterpolation filter is designed based on resource elements allocationpattern of a positioning signal, as shown in FIG. 5F. Specifically, onereason why a 11-tap triangular filter is used in such embodiments is dueto a frequency re-use factor of 6 for a PRS signal (in conformance withLTE), in the frequency domain. Moreover, in some embodiments use acell-specific gold code, to recreate interfering signals in acts426A-426N (FIG. 4), for example as described in 3^(rd) GenerationPartnership Project (3GPP), standard 36.211 Section 6.10.4.1. Hence,certain embodiments simply reverse a normal process of PRS symbol andsub-frame processing in conformance with LTE (which is normallyperformed on initial positioning measurements), to regenerateinterfering signals. To re-state, interference estimation in suchembodiments is simply a reverse procedure, of normal PRS processing inconformance with LTE. Also, several embodiments of the type describedherein use initial positioning measurements, of positioning signals, tomeasure channel energy response (CER), and use SNR of the CER toidentify a specific positioning signal as interfering in anidentification operation to determine whether to perform interferenceestimation and mitigation (or to not perform it), e.g. as illustrated inFIG. 2 (see acts 203, and 204 on how to identify a strong interferingpositioning signal, using SNRs).

Moreover, although a test of interference, which is based onthreshold-checking SNRs of multiple stations, is applied to initialpositioning measurements which are measured in one or more earliercyclical period(s) in certain embodiments, in alternative embodimentsthe just-described SNR-based test of interference may be applied toinitial positioning measurements of positioning signals which aremeasured in the current cyclical period (e.g. in first and secondsubframes of a positioning occasion), followed by use of identificationof an interfering station in interference estimation and mitigation asdescribed above (e.g. in third and fourth subframes of the samepositioning occasion, assuming N_(PRS)≧4). In such embodiments,interference identification, interference estimation and mitigation, maybe performed all within a single cyclical period (e.g. of durationN_(PRS)) in which positioning signals are received.

An example of user equipment (UE) in which various aspects of thedisclosure may be implemented will now be described in reference to acomputer system illustrated in FIG. 6. According to one or more aspects,a computer system as illustrated in FIG. 6 may be incorporated as partof an electronic device, which may implement, perform, and/or executeany and/or all of the features, methods, and/or method steps describedherein. For example, computer system 1000 may represent some of thecomponents of a hand-held device, such as UE 150 of FIG. 1A or UE 200 ofFIG. 2. A hand-held device may be any computing device with an inputsensory unit, such as a wireless receiver or modem. Examples of ahand-held device include but are not limited to video game consoles,tablets, smart phones, televisions, and mobile devices or mobilestations. In some embodiments, the computer system 1000 is configured toimplement any of the methods described above.

FIG. 6 provides a schematic illustration of one embodiment of userequipment in the form of a computer system 1000 that can perform themethods provided by various other embodiments, as described herein,and/or can function as the host computer system, a remotekiosk/terminal, a point-of-sale device, a mobile device, a set-top box,and/or a computer system. FIG. 6 is meant only to provide a generalizedillustration of various components, any and/or all of which may beutilized as appropriate. FIG. 6, therefore, broadly illustrates howindividual system elements may be implemented in a relatively separatedor relatively more integrated manner in a UE.

The computer system 1000 is shown comprising hardware elements that canbe electrically coupled via a bus 1005 (or may otherwise be incommunication, as appropriate). The hardware elements may include one ormore processor(s) 1010, including without limitation one or moregeneral-purpose processors and/or one or more special-purpose processors(such as digital signal processing chips, graphics accelerationprocessors, and/or the like); one or more input devices 1015, which caninclude without limitation a camera, wireless receivers, wirelesssensors, a mouse, a keyboard and/or the like; and one or more outputdevices 1020, which can include without limitation a display unit, aprinter and/or the like. In some embodiments, the one or moreprocessor(s) 1010 may be configured to perform a subset or all of thefunctions described above with respect to FIG. 2. The processor(s) 1010may comprise a general processor and/or and application processor, forexample. In some embodiments, the processor is integrated into anelement that processes visual tracking device inputs and wireless sensorinputs.

The computer system 1000 may further include (and/or be in communicationwith) one or more non-transitory storage devices, e.g. storage device1025, which can comprise, without limitation, local and/or networkaccessible storage, and/or can include, without limitation, a diskdrive, a drive array, an optical storage device, a solid-state storagedevice such as a random access memory (“RAM”) and/or a read-only memory(“ROM”), which can be programmable, flash-updateable and/or the like.Such storage devices may be configured to implement any appropriate datastorage, including without limitation, various file systems, databasestructures, and/or the like.

The computer system 1000 might also include a communications subsystem1030, which can include without limitation a modem, a network card(wireless or wired), an infrared communication device, a wirelesscommunication device and/or chipset (such as an 802.11 device, a WiFidevice, a WiMax device, cellular communication facilities, etc.), and/orthe like. The communications subsystem 1030 may permit data to beexchanged with a network (such as the network described below, to nameone example), other computer systems, and/or any other devices describedherein. In many embodiments, the computer system 1000 will furthercomprise a non-transitory working memory, e.g. memory 1035, which caninclude a RAM or ROM device, as described above. In some embodiments,the communications subsystem 1030 may interface with wirelesstransceiver(s) 1050 configured to transmit and receive signalswirelessly from access points and/or mobile devices and/or basestations. Some embodiments may include a separate receiver or receivers,and a separate transmitter or transmitters.

The computer system 1000 also can comprise software elements, shown asbeing currently located within memory 1035, including an operatingsystem 1040, device drivers, executable libraries, and/or other code,such as one or more application programs 1045, which may comprisecomputer programs provided by various embodiments, and/or may bedesigned to implement methods, and/or configure systems, provided byother embodiments, as described herein. Merely by way of example, one ormore procedures described with respect to the method(s) discussed above,for example as described with respect to FIG. 2, might be implemented ascode and/or instructions executable by a computer (and/or a processorwithin a computer); in an aspect, then, such code and/or instructionscan be used to configure and/or adapt a general purpose computer (orother device) to perform one or more operations in accordance with thedescribed methods.

A set of these instructions and/or code might be stored on acomputer-readable storage medium, such as the storage device(s) 1025described above. In some cases, the storage medium might be incorporatedwithin a computer system, such as computer system 1000. In otherembodiments, the storage medium might be separate from a computer system(e.g., a removable medium, such as a compact disc), and/or provided inan installation package, such that the storage medium can be used toprogram, configure and/or adapt a general purpose computer with theinstructions/code stored thereon. These instructions might take the formof executable code, which is executable by the computer system 1000and/or might take the form of source and/or installable code, which,upon compilation and/or installation on the computer system 1000 (e.g.,using any of a variety of generally available compilers, installationprograms, compression/decompression utilities, etc.) then takes the formof executable code.

Substantial variations may be made in accordance with specificrequirements. For example, customized hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

Some embodiments may employ a computer system (such as the computersystem 1000) to perform methods in accordance with the disclosure. Forexample, some or all of the procedures of the described methods may beperformed by the computer system 1000 in response to processor(s) 1010executing one or more sequences of one or more instructions (which mightbe incorporated into the operating system 1040 and/or other code, suchas an application program(s) 1045) contained in memory 1035. Suchinstructions may be read into memory 1035 from another computer-readablemedium, such as one or more of the storage device(s) 1025. Merely by wayof example, execution of the sequences of instructions contained inmemory 1035 might cause the processor(s) 1010 to perform one or moreprocedures of the methods described herein, for example methodsdescribed with respect to FIG. 6.

The terms “machine-readable medium” and “computer-readable medium,” asused herein, refer to any non-transitory medium that participates inproviding data that causes a machine to operate in a specific fashion.In an embodiment implemented using the computer system 1000, variousnon-transitory computer-readable media might be involved in providinginstructions/code to processor(s) 1010 for execution and/or might beused to store and/or carry such instructions/code (e.g., as signals).Non-transitory computer-readable media include, for example, opticaland/or magnetic disks, such as storage device(s) 1025. Non-transitorycomputer-readable media also include dynamic memory, such as memory1035.

In many implementations, a non-transitory computer-readable medium is aphysical and/or tangible storage medium. Common forms of physical and/ortangible media that are computer readable include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, or any other magneticmedium, a CD-ROM, any other optical medium, any other physical mediumwith patterns, a RAM, a PROM, EPROM, a FLASH-EPROM, any other memorychip or cartridge or any other non-transitory medium from which acomputer can read instructions and/or code.

Various forms of computer-readable media may be involved in carrying oneor more sequences of one or more instructions to the processor(s) 1010for execution. Merely by way of example, the instructions may initiallybe carried on a magnetic disk and/or optical disc of a remote computer.A remote computer might load the instructions into its dynamic memoryand send the instructions as signals over a transmission medium to bereceived and/or executed by the computer system 1000. These signals,which might be in the form of electromagnetic signals, acoustic signals,optical signals and/or the like, are all examples of carrier waves onwhich instructions can be encoded, in accordance with variousembodiments of the invention. Transmission media include, withoutlimitation, coaxial cables, copper wire and fiber optics, including thewires that comprise the bus 1005, as well as the various components ofthe communications subsystem 1030 (and/or the media by which thecommunications subsystem 1030 provides communication with otherdevices).

The communications subsystem 1030 (and/or components thereof) generallyreceive signals, and bus 1005 might carry the signals (and/or the data,instructions, etc. carried by the signals) to memory 1035, from whichthe processor(s) 1010 retrieves and executes the instructions. Theinstructions received by memory 1035 may optionally be stored on anon-transitory storage device(s) 1025 either before or after executionby the processor(s) 1010. Memory 1035 may contain at least one databaseaccording to any of the databases and methods described herein. Memory1035 may thus store any of the values discussed in any of the presentdisclosures, including FIG. 2 and related descriptions, such as TDOAmeasurements, and thresholds Th1, Th2.

The methods described in FIGS. 1C and 2 may be implemented by variousblocks in FIG. 6. For example, processor(s) 1010 may be configured byinstructions and data to perform any of the functions of acts andoperations in method 400 (FIG. 4). Storage device 1025 may be configuredto store an intermediate result, such as frequency domain channelresponse and channel impulse response discussed within any of blocksmentioned herein. Storage device 1025 may also contain a databaseconsistent with any of the present disclosures. The memory 1035 maysimilarly be configured to record signals, representation of signals, ordatabase values necessary to perform any of the functions described inany of the blocks mentioned herein. Results that may need to be storedin a non-transitory memory, such as RAM, may also be included in memory1035, and may include any intermediate result similar to what may bestored in storage device 1025, such as, frequency domain channelresponse and channel impulse response. Input device(s) 1015 may beconfigured to receive wireless signals from satellites and/or basestations according to the present disclosures described herein. Outputdevice(s) 1020 may be configured to display images, print text, transmitsignals and/or output other data according to any of the presentdisclosures.

In some embodiments, continuing to measure positioning signals in aparticular cyclical period (e.g. one of the positioning occasions thatoccur repeatedly, at a periodicity defined by a period T_(PRS)), whilesimultaneously mitigating (e.g., reducing, canceling, etc.) one or moretones by a UE enables detection of one or more weak positioning signalsthat are otherwise undetectable. In certain embodiments, estimation andmitigation of strong positioning signals are performed within a singlesubframe I of the particular positioning occasion within a radio frameof period T_(PRS) in the LTE signal, wherein Δ_(PRS)≦I<Δ_(PRS)+N_(PRS).Thus, multiple PRS signals from corresponding multiple base stations maybe measured within the same Observed Time Difference of Arrival (OTDOA)session even when one or more strong cells interfere with one or moreweak cells, and measurements from strong cell(s) and weak cell(s) may beused together, to determine Reference Signal Time Difference (RSTD), andthe RSTD used to determine the UE's position.

In some embodiments, wireless transceiver(s) 1050 configured to transmitand receive signals wirelessly, may implement means for measuring aplurality of positioning signals that are synchronized relative to oneanother, to obtain initial positioning measurements. In several suchembodiments, processor(s) 1010 configured to execute a first sequence ofone or more instructions contained in memory 1035 implement means forapplying a test of interference to the initial positioning measurementsmeasured within a current cyclical period (e.g. a specific positioningoccasion of N_(PRS) subframes) in a transmission schedule of positioningsignals (e.g. in accordance with LTE), to identify one or moreinterfering station(s). Moreover, in several such embodiments,processor(s) 1010 configured to execute a second sequence of one or moreinstructions contained in memory 1035 implement means for estimating afirst plurality of tones of one or more interfering station(s), based onthe initial positioning measurements measured in the current cyclicalperiod. In several such embodiments, processor(s) 1010 configured toexecute a third sequence of one or more instructions contained in memory1035 implement means for mitigating the first plurality of tones of oneor more interfering station(s), from the initial positioningmeasurements in the current cyclical period, to obtain modifiedpositioning measurements measured in the current cyclical period.Moreover, in some embodiments, processor(s) 1010 configured to execute afourth sequence of one or more instructions contained in memory 1035implement means for determining a first plurality of arrival times atthe apparatus, based on initial positioning measurements of positioningsignals (e.g. from one or more interfering station(s)). And, in someembodiments, processor(s) 1010 configured to execute a fifth sequence ofone or more instructions contained in memory 1035 implement means fordetermining a second plurality of arrival times at the apparatus, basedon modified positioning measurements of positioning signals (e.g. fromone or more weak station(s)). Finally, in some embodiments, processor(s)1010 configured to execute a sixth sequence of one or more instructionscontained in memory 1035 to implement means for using the firstplurality of arrival times and the second plurality of arrival times, tocompute and store in one or more non-transitory computer readablestorage media, the position of the apparatus.

Accordingly, several embodiments of the type described herein do notrely on coefficient correlation or TOA estimate to identify aninterfering signal. Instead, as noted above, a test for interference insuch embodiments uses signal-to-noise ratios (SNRs) based on initialpositioning measurements. More specifically, some embodiments checkwhether the SNR of the strongest signal exceeds one threshold Th1 andwhether the SNR of one or more weak signals falls below anotherthreshold Th2, to determine whether or not to perform interferenceestimation and interference mitigation, on initial positioningmeasurements. As noted above, the initial positioning measurements overwhich interference estimation and mitigation are performed, are measuredwithin a single cyclical period (e.g. within the duration of a singlepositioning occasion) in many embodiments to ensure that interferenceestimates do not become stale and unreliable, e.g. over a time lapse of160 milliseconds (or any such duration of T_(PRS) subframes). Thus, suchembodiments do not estimate interference in a first positioningoccasion, and subsequently mitigate interference in a second positioningoccasion (because separation by a duration of T_(PRS) subframes or moreresults in loss of accuracy, and unreliability).

The methods, systems, and devices discussed above are examples. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods described may be performed in an order different from thatdescribed, and/or various stages may be added, omitted, and/or combined.Also, features described with respect to certain embodiments may becombined in various other embodiments. Different aspects and elements ofthe embodiments may be combined in a similar manner. Also, technologyevolves and, thus, many of the elements are examples that do not limitthe scope of the disclosure to those specific examples.

Specific details are given in the description to provide a thoroughunderstanding of various embodiments. However, embodiments may bepracticed without these specific details. For example, well-knowncircuits, processes, algorithms, structures, and techniques have beenshown without unnecessary detail in order to avoid obscuring theembodiments. This description provides example embodiments only, and isnot intended to limit the scope, applicability, or configuration of theinvention. Rather, the preceding description of the embodiments willprovide those skilled in the art with an enabling description forimplementing embodiments of the invention. Various changes may be madein the function and arrangement of elements without departing from thespirit and scope of the invention.

Also, some embodiments were described as processes depicted as flowdiagrams or block diagrams. Although each may describe certain acts as asequential process, many of the acts can be performed in parallel orconcurrently. In addition, the order of some acts may be rearranged,although interference estimation in act 182 must be performed beforeinterference mitigation in act 184. A process may have additional stepsnot included in the figure. Furthermore, embodiments of the methods maybe implemented by hardware, software, firmware, middleware, microcode,hardware description languages, or any combination thereof. Whenimplemented in software, firmware, middleware, or microcode, the programcode or code segments to perform the associated tasks may be stored in acomputer-readable medium such as a storage medium. Processors mayperform the associated tasks.

Having described several embodiments, various modifications, alternativeconstructions, and equivalents may be used without departing from thespirit of the disclosure. For example, the above elements may merely bea component of a larger system, wherein other rules may take precedenceover or otherwise modify the application of the invention. Also, anumber of steps may be undertaken before, during, or after the aboveelements are considered. Accordingly, the above description does notlimit the scope of the disclosure.

Various examples have been described. These and other examples arewithin the scope of the following claims.

The invention claimed is:
 1. A method for use in determining a positionof a user equipment, the method comprising: measuring, by a wirelesstransceiver in the user equipment, a plurality of positioning signalsthat are synchronized relative to one another, to obtain initialpositioning measurements; estimating, by a processor in the userequipment, a first plurality of tones of one or more interferingstation(s), based on the initial positioning measurements measured in acurrent cyclical period during which positioning signals are transmittedper a transmission schedule, and based on identification of the one ormore interfering station(s); mitigating, by the processor in the userequipment, the first plurality of tones of one or more interferingstation(s), from the initial positioning measurements measured in thecurrent cyclical period, to obtain modified positioning measurements ofthe current cyclical period; determining, by the processor in the userequipment, a first plurality of arrival times at the user equipment,based at least on the initial positioning measurements; determining, bythe processor in the user equipment, a second plurality of arrival timesat the user equipment, based at least on the modified positioningmeasurements; and computing, by the processor in the user equipment, aposition of the user equipment based, at least in part, on the firstplurality of arrival times and the second plurality of arrival times. 2.The method of claim 1 wherein the current cyclical period has a durationof a predetermined number of subframes N_(PRS) which are grouped into apositioning occasion, in the transmission schedule.
 3. The method ofclaim 1 further comprising: applying, by the processor in the userequipment, a test of interference to additional initial positioningmeasurements measured in one or more earlier cyclical periods, toidentify the one or more interfering station(s) prior to the currentcyclical period.
 4. The method of claim 3 wherein the test ofinterference comprises: determining whether a signal-to-noise ratio of apositioning signal from a strongest station is greater than a firstthreshold; and determining whether another signal-to-noise ratio ofanother positioning signal from another station is less than a secondthreshold.
 5. The method of claim 1 wherein: the modified positioningmeasurements obtained in a first subframe within the current cyclicalperiod are integrated with the modified positioning measurementsobtained in a second subframe within the current cyclical period.
 6. Themethod of claim 1 wherein mitigating of the first plurality of tones ofone or more interfering station(s) comprises: scaling tones of the oneor more interfering station(s), opposite to a direction used in symbolprocessing to obtain a plurality of unscaled tones; rotating theplurality of unscaled tones in a direction inverse of symbol processingto obtain a plurality of unrotated tones; scrambling the plurality ofunrotated tones with a predetermined seed to obtain a plurality ofreconstructed tones; and subtracting the plurality of reconstructedtones from positioning signals measured by the wireless transceiver, toobtain the modified positioning measurements.
 7. The method of claim 1wherein estimation of the first plurality of tones of one or moreinterfering station(s) comprises: scaling each first tap of a vector ofchannel impulse response (CIR) of the initial positioning measurements,with relative signal strength over signal-plus-noise level, to obtain awindowed CIR vector; comparing energy of each second tap of the windowedCIR vector with a predetermined noise threshold and zeroing out aspecific second tap if the specific second tap does not exceed thepredetermined noise threshold, to obtain a cleaned CIR vector; settingto zero, a plurality of values in the cleaned CIR vector outside awindow of a predetermined duration, the window being centered at a mainpeak in the cleaned CIR vector, to obtain a pruned CIR vector; addingzero values to the pruned CIR vector that are sufficient in number, toobtain an improved CIR vector of a length determined by a predeterminedfourier transform; and applying the predetermined fourier transform tothe improved CIR vector, to obtain and store in memory the firstplurality of tones of one or more interfering station(s).
 8. The methodof claim 1 wherein estimation of the first plurality of tones of one ormore interfering station(s) comprises: searching for a peak in a vectorof channel impulse response (CIR) of positioning signals; aligning thepeak to origin, by performing a circular shift using frequency domainchannel response of positioning signals, to obtain an origin-centeredCIR vector; eliminating aliasing in the origin-centered CIR vector byfrequency interpolation, to obtain an interpolated CIR vector; scalingthe interpolated CIR vector to overcome energy diminishment caused byzero tones, to obtain a scaled CIR vector; and performing on the scaledCIR vector, reverse of the circular shift, to obtain and store in memorythe first plurality of tones of one or more interfering station(s).
 9. Anon-transitory computer-readable storage media comprising a plurality ofinstructions that are executable by a processor in a user equipment todirect the user equipment to: measure strengths of positioning signalsthat are synchronized relative to one another, to obtain initialpositioning measurements; estimate a first plurality of tones of one ormore interfering station(s), based on the initial positioningmeasurements measured in a current cyclical period during whichpositioning signals are transmitted per a transmission schedule, andbased on identification of the one or more interfering station(s);mitigate the first plurality of tones of one or more interferingstation(s to obtain modified positioning measurements of the currentcyclical period; determine a first plurality of arrival times at theuser equipment, based at least on the initial positioning measurements;determine a second plurality of arrival times at the user equipment,based at least on the modified positioning measurements; and compute aposition of the user equipment based, at least in part, on the firstplurality of arrival times and the second plurality of arrival times.10. The non-transitory computer-readable storage media of claim 9wherein the current cyclical period has a duration of a predeterminednumber of subframes N_(PRS) which are grouped into a positioningoccasion, in the transmission schedule.
 11. The non-transitorycomputer-readable storage media of claim 9, wherein the instructions arefurther executable by the processor to direct the user equipment to:apply a test of interference to additional initial positioningmeasurements measured in one or more earlier cyclical periods, toidentify the one or more interfering station(s) prior to the currentcyclical period.
 12. The non-transitory computer-readable storage mediaof claim 11 wherein the instructions are further executable by theprocessor to direct the user equipment, as part of the test ofinterference, to: determine whether a signal-to-noise ratio of apositioning signal from a strongest station is greater than a firstthreshold; and determine whether another signal-to-noise ratio ofanother positioning signal from another station is less than a secondthreshold.
 13. The non-transitory computer-readable storage media ofclaim 9, wherein the instructions are further executable by theprocessor to direct the user equipment to: integrate the modifiedpositioning measurements obtained in a first subframe within the currentcyclical period with the modified positioning measurements obtained in asecond subframe within the current cyclical period.
 14. Thenon-transitory computer-readable storage media of claim 9 wherein theinstructions are further executable by the processor to direct the userequipment to: scale, the first plurality of tones of one or moreinterfering station(s), opposite to a direction used in symbolprocessing to obtain a plurality of unscaled tones; rotate the pluralityof unscaled tones in a direction inverse of symbol processing to obtaina plurality of unrotated tones; scramble the plurality of unrotatedtones with a predetermined seed to obtain a plurality of reconstructedtones; and subtract the plurality of reconstructed tones from aplurality of tones output by execution of the instructions to measurepositioning signals, to obtain the modified positioning measurements.15. The non-transitory computer-readable storage media of claim 9,wherein the instructions are further executable by the processor todirect the user equipment to: scale each first tap of a vector ofchannel impulse response (CIR) of positioning signals, with relativesignal strength over signal-plus-noise level, to obtain a windowed CIRvector; compare energy of each second tap of the windowed CIR vectorwith a predetermined noise threshold and zeroing out a specific secondtap if the specific second tap does not exceed the predetermined noisethreshold, to obtain a cleaned CIR vector; set to zero, a plurality ofvalues in the cleaned CIR vector outside a window of a predeterminedduration, the window being centered at a main peak in the cleaned CIRvector, to obtain a pruned CIR vector; add zero values to the pruned CIRvector that are sufficient in number, to obtain an improved CIR vectorof a length determined by a predetermined fourier transform; and applythe predetermined fourier transform to the improved CIR vector, toobtain and store in memory the first plurality of tones of one or moreinterfering station(s).
 16. The non-transitory computer-readable storagemedia of claim 9, wherein the instructions are further executable by theprocessor to direct the user equipment to: search for a peak in a vectorof channel impulse response (CIR) of positioning signals; align the peakto origin by performing a circular shift using frequency domain channelresponse of positioning signals, to obtain an origin-centered CIRvector; eliminate aliasing in the origin-centered CIR vector byfrequency interpolation, to obtain an interpolated CIR vector; scale theinterpolated CIR vector to overcome energy diminishment caused by zerotones, to obtain a scaled CIR vector; and perform on the scaled CIRvector, reverse of the circular shift, to obtain and store in memory thefirst plurality of tones of one or more interfering station(s).
 17. Adevice comprising: a wireless transceiver; a memory; a processoroperatively coupled to the wireless transceiver and the memory, andwherein the processor and the memory are configured to: obtain initialpositioning measurements from the wireless transceiver, the initialsignal strength measurements corresponding to measured strengths ofpositioning signals that are synchronized relative to one another;estimate a first plurality of tones of one or more interferingstation(s), based on the initial positioning measurements measured in acurrent cyclical period during which positioning signals are transmittedper a transmission schedule, and based on identification of the one ormore interfering station(s); mitigate the first plurality of tones ofone or more interfering station(s), from the initial positioningmeasurements measured in the current cyclical period, to obtain modifiedpositioning measurements of the current cyclical period; determine afirst plurality of arrival times at the device, based at least on theinitial positioning measurements; determine a second plurality ofarrival times at the device, based at least on the modified positioningmeasurements; and determine a position of the user device based, atleast in part, on the first plurality of arrival times and the secondplurality of arrival times.
 18. The device of claim 17 wherein thecurrent cyclical period has a duration of a predetermined number ofsubframes N_(PRS) which are grouped into a positioning occasion, in thetransmission schedule.
 19. The device of claim 17 wherein the processorand the memory are further configured to: apply a test of interferenceto additional initial positioning measurements measured in one or moreearlier cyclical periods, to identify the one or more interferingstation(s) prior to the current cyclical period.
 20. The device of claim19 wherein, as part of the test of interference, the processor and thememory are further configured to: determine of whether a signal-to-noiseratio of a positioning signal from a strongest station is greater than afirst threshold; and determine of whether another signal-to-noise ratioof another positioning signal from another station is less than a secondthreshold.
 21. The device of claim 17 wherein to mitigate the firstplurality of tones of one or more interfering station(s), the processorand the memory are further configured to: scale tones of the one or moreinterfering station(s), opposite to a direction used in symbolprocessing to obtain a plurality of unscaled tones; rotate the pluralityof unscaled tones in a direction inverse of symbol processing to obtaina plurality of unrotated tones; scramble the plurality of unrotatedtones with a predetermined seed to obtain a plurality of reconstructedtones; and subtract the plurality of reconstructed tones frompositioning signals measured by the wireless transceiver, to obtain themodified positioning measurements.
 22. The device of claim 17 wherein toestimate the first plurality of tones of one or more interferingstation(s), the processor and the memory are further configured to:scale each first tap of a vector of channel impulse response (CIR) ofthe initial positioning measurements, with relative signal strength oversignal-plus-noise level, to obtain a windowed CIR vector; compare energyof each second tap of the windowed CIR vector with a predetermined noisethreshold and zeroing out a specific second tap if the specific secondtap does not exceed the predetermined noise threshold, to obtain acleaned CIR vector; set to zero, a plurality of values in the cleanedCIR vector outside a window of a predetermined duration, the windowbeing centered at a main peak in the cleaned CIR vector, to obtain apruned CIR vector; add zero values to the pruned CIR vector that aresufficient in number, to obtain an improved CIR vector of a lengthdetermined by a predetermined fourier transform; and apply thepredetermined fourier transform to the improved CIR vector, to obtainand store the first plurality of tones of one or more interferingstation(s).
 23. The device of claim 17 wherein to estimate the firstplurality of tones of one or more interfering station(s), the processorand the memory are further configured to: search for a peak in a vectorof channel impulse response (CIR) of positioning signals; align the peakto origin, by performing a circular shift using frequency domain channelresponse of positioning signals, to obtain an origin-centered CIRvector; eliminate aliasing in the origin-centered CIR vector byfrequency interpolation, to obtain an interpolated CIR vector; scale theinterpolated CIR vector to overcome energy diminishment caused by zerotones, to obtain a scaled CIR vector; and perform on the scaled CIRvector, reverse of the circular shift, to obtain and store the firstplurality of tones of one or more interfering station(s).
 24. Anapparatus for use in a user equipment to determine a position of theuser equipment, the apparatus comprising: means for measuring aplurality of positioning signals that are synchronized relative to oneanother, to obtain initial positioning measurements; means forestimating a first plurality of tones of one or more interferingstation(s), based on the initial positioning measurements measured in acurrent cyclical period during which positioning signals are transmittedin a transmission schedule, and based on identification of the one ormore interfering station(s); means for mitigating the first plurality oftones of one or more interfering station(s), from the initialpositioning measurements in the current cyclical period, to obtainmodified positioning measurements of the current cyclical period; meansfor determining a first plurality of arrival times at the apparatus,based at least on the initial positioning measurements; means fordetermining a second plurality of arrival times at the apparatus, basedat least on the modified positioning measurements; and means determininga position of the user equipment based, at least in part, on the firstplurality of arrival times and the second plurality of arrival.
 25. Theapparatus of claim 24 wherein the current cyclical period has a durationof a predetermined number of subframes N_(PRS) which are grouped into apositioning occasion, in the transmission schedule.
 26. The apparatus ofclaim 24 further comprising: means for applying a test of interferenceto additional initial positioning measurements measured in one or moreearlier cyclical periods, to identify the one or more interferingstation(s) prior to the current cyclical period.
 27. The apparatus ofclaim 26 wherein the test of interference comprises: means fordetermining whether a signal-to-noise ratio of a positioning signal froma strongest station is greater than a first threshold; and means fordetermining whether another signal-to-noise ratio of another positioningsignal from another station is less than a second threshold.
 28. Theapparatus of claim 24 wherein the means for mitigating the firstplurality of tones of one or more interfering station(s) comprises:means for scaling tones of the one or more interfering station(s),opposite to a direction used in symbol processing to obtain a pluralityof unscaled tones; means for rotating the plurality of unscaled tones ina direction inverse of symbol processing to obtain a plurality ofunrotated tones; means for scrambling the plurality of unrotated toneswith a predetermined seed to obtain a plurality of reconstructed tones;and means for subtracting the plurality of reconstructed tones frompositioning signals, to obtain the modified positioning measurements.29. The apparatus of claim 24 wherein the means for estimating the firstplurality of tones of one or more interfering station(s) comprises:means for scaling each first tap of a vector of channel impulse response(CIR) of the initial positioning measurements, with relative signalstrength over signal-plus-noise level, to obtain a windowed CIR vector;means for comparing energy of each second tap of the windowed CIR vectorwith a predetermined noise threshold and zeroing out a specific secondtap if the specific second tap does not exceed the predetermined noisethreshold, to obtain a cleaned CIR vector; means for setting to zero, aplurality of values in the cleaned CIR vector outside a window of apredetermined duration, the window being centered at a main peak in thecleaned CIR vector, to obtain a pruned CIR vector; means for adding zerovalues to the pruned CIR vector that are sufficient in number, to obtainan improved CIR vector of a length determined by a predetermined fouriertransform; and means for applying the predetermined fourier transform tothe improved CIR vector, to obtain and store in memory the firstplurality of tones of one or more interfering station(s).
 30. Theapparatus of claim 24 wherein the means for estimating the firstplurality of tones of one or more interfering station(s) comprises:means for searching for a peak in a vector of channel impulse response(CIR) of positioning signals; means for aligning the peak to origin, byperforming a circular shift using frequency domain channel response ofpositioning signals, to obtain an origin-centered CIR vector; means foreliminating aliasing in the origin-centered CIR vector by frequencyinterpolation, to obtain an interpolated CIR vector; means for scalingthe interpolated CIR vector to overcome energy diminishment caused byzero tones, to obtain a scaled CIR vector; and means for performing onthe scaled CIR vector, a reverse of the circular shift, to obtain andstore in memory the first plurality of tones of one or more interferingstation(s).